1. Field of the Invention
The present invention relates to an apparatus and method for sensing a laundry amount in a washing machine, and more particularly, to an apparatus and method for sensing a laundry amount in a washing machine which is capable of improving the degree of sensing of the laundry amount to heighten an efficiency of a washing machine by controlling a current and detecting a speed to reduce an error of sensing the amount of the laundry caused due to an inconstant common AC power supply especially in an inverter washing machine using a brushless DC (BLDC) motor.
2. Description of the Background Art
Recently, in view of improving a cleaning degree and reducing noise and energy consumption, washing machines mostly adopt an inverter which is able to control the speed of a motor therein. The operations of such a conventional washing machine will now be described with reference to the accompanying drawings.
FIG. 1 is a schematic circuit diagram showing the construction of a general BLDC motor driving apparatus in the conventional art.
As shown in the drawing, the BLDC motor driving apparatus includes a rectifier 10 receiving a common AC power supply voltage and rectifying it to a DC voltage, an inverter 20 receiving the DC voltage from the rectifier 10 through a smoothing capacitor C1 and converting it to a three-phase AC voltage according to gate drive signals from a gate driving unit 60 to be described, a BLDC motor 30 driven by the three-phase AC voltage from the inverter 20, a rotor position detector 40 detecting the position of a rotor of the BLDC motor 30, a microcomputer 50 receiving a position detect signal from the rotor position detector 40 and outputting a control signal according to the position detect signal, and the gate driving unit 60 receiving the control signal from the microcomputer 50 and outputting the gate drive signals to the inverter 20 in response to the control signal.
The operation of the BLDC motor driving apparatus constructed as described above will now be explained.
First, the rectifier 10 rectifies a common AC power supply voltage and outputs the DC voltage. The outputted DC voltage is smoothed by the smoothing capacitor and applied to the inverter 20.
Upon receipt of the DC voltage, the inverter 20 converts it to a three-phase AC voltage and drives the BLDC motor 30 with the three-phase AC voltage according to the gate drive signal from the gate driving unit 60.
At this time, the rotor position detector 40 detects the position of the rotor of the BLDC motor 30 by using a position sensor and applies it to the microcomputer 50.
Upon receipt of the position detect signal from the rotor position detector 40, the microcomputer 50 applies the control signal generated according to the position detect signal, according to which the gate driving unit 60 receives the control signal and applies the gate drive signals to the inverter 20 in response to the control signal.
Thereafter, the operations as described above are repeatedly performed to control driving of the BLDC motor 30.
In order to effectively control a washing/rinsing stroke, an inverter washing machine adopting the BLDC motor which performs the above operations should accurately detect the weight of the laundry, that is, the amount of the laundry.
There are two methods for sensing the amount of the laundry; one is to sense the amount of the laundry in such a manner that the motor is accelerated to a predetermined speed for a certain time period and then the power supply is cut off, during which the deceleration time period, that is, corresponding to the inertia according to the amount of the laundry; and the other is to sense the amount of the laundry by measuring the time taken to accelerate the motor to a certain speed.
Generally, the conventional system in which a pulsator receives a rotational force from a motor via a clutch and a gear or changes a direction adopts the method for sensing the amount of the laundry by measuring the inertia according to the amount of the laundry.
Meanwhile, in the case of a direct drive washing system in which a pulsator or a washing tub is driven by being directly connected with a motor, the time taken to accelerate the motor to a certain speed is measured to sense the amount of the laundry.
As shown in FIGS. 2A through 2E, the motor is initially positioned at a reference point and then the strength of a voltage applied to the motor is regularly increased. This is possible by controlling an inverter switch of the inverter 20 at an appropriate duty ratio as shown in FIG. 2A.
With reference to FIG. 2B which shows the amplitude of a voltage applied to the motor, when the duty ratio is increased, the interval where the inverter is switched on is extended. Thus, it is noted that an average value of the voltage applied to the motor becomes gradually higher as time goes by.
With reference to FIG. 2A, if the amount of the laundry is greater than a reference amount of the laundry, since the motor must develop more torque to reach a certain reference speed or a reference position, a longer time is taken compared to a reference time.
Conversely, if the amount of the laundry is less than the reference amount, the motor needs less energy, and thus, it reaches the reference speed or the reference position within a shorter time than the reference time.
That is, as described above, the amount of the laundry can be detected by computing a time during which the motor or the washing tub reaches a certain speed or a certain position after a certain voltage is applied to the motor.
In this method for sensing the amount of the laundry, factors affecting the accuracy of the sensed amount of the laundry include mechanical factors such as the deflection of a bearing housing, the vibration or imbalance or shaking of a washing tub and the deflection of a damper, motor factors such as the inductance and a rotor position sensing Hall-effect sensor, the factor of a voltage detector, the factor of a voltage variation and the factor of a control circuit vibration due to temperature, etc.
Among those factors, the most influential factor is the voltage detecting error caused due to a variation of the source voltage.
That is, in the case that the amount of the laundry is sensed by the time necessary for reaching a certain reference speed or a certain reference position, a certain source voltage is to be applied regardless of the amount of the laundry or the circumstances. If a certain source voltage is not applied according to the circumstances, the computed value of the amount of the laundry will exhibit a large error from an actual value.
FIGS. 3A through 3E are signal waveforms exhibiting an error in detecting the amount of the laundry in the case that a certain source voltage is not applied to the motor.
As shown in FIGS. 3B and 3D, in the case that, for the same laundry amount, if the source voltage is higher than the reference voltage, if the source voltage applied to the motor in a certain duty ratio is increased, more voltage than the reference voltage would be applied to the motor, so that the motor can reach the reference speed or the reference position earlier than the reference time.
That is, as the motor reaches the reference speed or position earlier than the reference time to by as much as xcex94t1, a laundry amount sensing error is generated corresponding to the time xcex94t1. Conversely, in the case that the source voltage is lower than the reference voltage, the motor reaches the reference speed later by as much as xcex94t2, so that it is detected that there is a greater laundry amount than the actual laundry amount corresponding to the time xcex94t2.
FIG. 3D shows an AC power source voltage variation and a corresponding variation of a voltage of a DC link terminal in an inverter. The DC link voltage directly affects an average AC voltage applied to the motor through the inverter.
In an effort to solve the laundry amount sensing error caused due to the variation of the source voltage, the DC link voltage is detected to compensate for the voltage applied to the motor.
In this case, however, the DC link voltage should be detected to be compensated on a real time basis, and due to property of the inner elements (the selection of an ideal element can obviate an error in the detected voltage) of the voltage detector or a deviation of a constant voltage regulated power supply for signal processing, there occurs an error in the detected voltage.
Therefore, an object of the present invention is to provide an apparatus for sensing the laundry amount in a washing machine which is capable of sensing accurately the laundry amount by controlling an applied current and a torque of a motor of the washing machine.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an apparatus for sensing a laundry amount in a washing machine including: an inverter receiving the DC voltage from the rectifier through a smoothing capacitor and converting it to a three-phase AC voltage, a BLDC motor driven by the three-phase AC voltage from the inverter, a rotor position detector detecting the position of a rotor of the BLDC motor; a microcomputer controlling a switching operation of the inverter according to the position detect signal from the rotor position detector; a gate driving unit receiving a control signal from the microcomputer and outputting a gate drive signal to the inverter; a torque command generator generating a torque command signal corresponding to a speed set by a user; a torque controller operating the torque command signal from the torque command generator and outputting a q-axis current command signal; a current controller applying a current control signal according to the q-axis current command signal from the torque controller and a d-axis current command signal from a current command unit to the inverter; a speed detector detecting a driving speed of the BLDC motor according to the position detect signal from the rotor position detector; a laundry amount sensor comparing the speed detect signal from the speed detector with a previously stored reference speed value and determining a laundry amount therefrom; and a current command unit applying the d-axis current command signal to the current controller according to the speed detect signal from the speed detector.
To achieve at least these advantages in whole or in parts, there is further provided a method for sensing a laundry amount in a washing machine including the steps of: receiving a torque command signal, operating it and outputting a q-axis current command signal; receiving the q-axis current command signal and a d-axis current command signal and outputting a corresponding current control signal; applying a three-phase AC voltage to a BLDC motor of the washing machine according to the current control signal and detecting a position of a rotor of the BLDC motor; receiving a position detect signal and detecting a driving speed of the BLDC motor accordingly; receiving the speed detect signal, comparing the speed detect signal with a previously stored reference speed value and sensing a laundry amount therefrom; and receiving the speed detect signal, comparing the speed detect signal with the previously stored reference speed value and outputting a d-axis current command signal.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.